The Brassie Hair Packer by Hareline is a specialized fly tying tool used when working with spun or stacked deer hair, helping you pack it tightly along the hook shank to create dense, clean bodies. After you spin or stack a clump of hair, you slide the packer over the hook and push the hair back firmly, compressing both the hair and thread together. This process is what gives flies like bass bugs, hoppers, and muddlers their tight, durable, and shapeable bodies.